nommu: use MAP_UNINITIALIZE for mallocs

nommu: use MAP_UNINITIALIZE for mallocs

Now that the kernel supports MAP_UNINITIALIZE, have the malloc places use
it to get real uninitialized memory on no-mmu systems.  This avoids a lot
of normally useless overhead involved in zeroing out all of the memory
(sometimes multiple times).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>